Ref ID : 805
George G. Holz, Jr.; The oxidative metabolism of a cryptomonad flagellate Chilomonas paramecium. Anonymous:114-120, 1953
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Tests based on respirometric and population growth methods for the analysis of oxidizable substrates for Chilomonas paramecium revealed that only those substrates tested which are intermediates in terminal cyclic respiratory mechanisms (pyruvate, lactate, acetate, alpha-ketoglutarate, succinate, fumarate, L-malate, oxalacetate, but not citrate, cis-aconitate or DL-isocitrate) were attacked. These organic acids, and the fatty acids and alcohols earlier known to be used, n-butyric, n-caproic and n-caprylic acids, ethyl, n-butyl and n-hexyl alcohols, were the only carbon compounds oxidized by C. paramecium under the test conditions employed. Utilization of acid substrates was found to be pH-dependent. Reproductive and respiratory rates were related to the pKa values of the compounds. Oxidation of acetate, lactate, and pyruvate, however, was observed at pH values where their molecular form was present in exceedingly small amounts. Naturally-occurring alpha-amino acids, amines, glycolysis intermediates (3-phosphoglyceric acid, glucose-1-phosphate, hexose diphosphate) and degraded intermediates of glycolysis (glyceric acid, glycerol, dihydroxyacetone, glucose), two-carbon compounds more oxidized than acetic acid (oxalic, glycolic, glyoxylic acids, glyoxal, ethylene glycol), and formic, tartaric, malonic, and glutaric acids, were not used. Respiration in the presence of single members of the group of oxidizable substrates was sensitive to malonate and fluoroacetate. Malonate inhibition of succinate oxidation could be reversed by an increase in succinate concentration, but the relationship was not competitive; possibly because of permeability differences between the substrate and inhibitor. Fluoroacetate inhibition was accompanied by the accumulation of citric acid. The experiments on substrate oxidation, and the effects of inhibitors on the respiratory metabolism of the flagellate, are considered to provide evidence for the operation of the Krebs tricarboxylic acid cycle as a terminal respiratory mechanism in C. paramecium.